1. Field of the Invention
This invention relates to a laminate polarizer which provides linearly polarized light having a high degree of polarization and is useful for improving visibility of a liquid crystal display, and the like.
The present application is based on Japanese Patent Application No. Hei. 11-117548 and 2000-73211, which are incorporated herein by reference.
2. Description of the Related Art
Dichroic polarizers having a dichroic substance, such as iodine, Herapathit, or a dichroic dye, adsorbed and orientated on a substrate are known. These polarizers have been frequently used in liquid crystal displays, etc. However, since the dichroic polarizers take advantage of light absorption by the dichroic substance, the resulting polarized light is usually partially polarized light. Use of such polarizers in a crossed-Nicol arrangement has involved the problem of light leakage.
Light leakage causes image contrast lower in a black display mode of a liquid crystal display. Where the concentration of adsorbed dichroic substance is increased to increase the light absorption thereby to reduce light leakage, the brightness in a white display mode considerably decreases, resulting in difficulty of improving the image visibility. The problem of reduction in visibility due to light leakage is particularly conspicuous to an extent not negligible for practical use in the case of dye-containing dichroic polarizers which are excellent in high temperature durability. The low dichroism of the dyes is also contributory to the problem.
Accordingly, an object of the present invention is to provide a polarizer which provides polarized light having a high polarization degree while minimizing light leakage in a crossed-Nicol arrangement thereby to provide a liquid crystal display having satisfactory visibility with improved contrast in a black display mode or improved brightness in a white display mode.
The present invention provides a laminate polarizer which comprises a dichroic polarizing sheet and a polarizing and scattering sheet which has anisotropy in light scattering properties depending on the direction of polarization, the absorption axis of the dichroic polarizing sheet and the optical axis of the polarizing and scattering sheet in which linearly polarized light is scattered most intensely being in parallel to each other.
The present invention also provides a liquid crystal display characterized by having the laminate polarizer as a polarizer on the light source side of the liquid crystal panel.
According to the present invention, the optical axis of the polarizing and scattering sheet in which linearly polarized light is transmitted efficiently (the direction in which linearly polarized light is hardly scattered) and the transmission axis of the dichroic polarizing sheet agree with each other. As a result, the laminate polarizer exhibits excellent transmission in that optical axis. On the other hand, the optical axis of the polarizing and scattering sheet which exhibits strong scattering properties for polarized light agrees with the absorption axis of the dichroic polarizing sheet, so that linearly polarized light is intensely scattered in this optical axis to reduce the transmittance. It follows that the laminate polarizer is, as a whole, capable of producing highly polarized light without being accompanied by large reduction in transmission.
Accordingly, a crossed-Nicol of the laminate polarizers hardly causes light leakage to provide a liquid crystal display and the like which have satisfactory visibility in terms of image contrast in a black display mode and brightness in a white display mode. The laminate polarizer of the invention can efficiently be produced simply by superposing the constituent layers on each other and is suited to mass production. Where the laminate polarizer is disposed on the light source side of the liquid crystal panel, hindrance to visibility attributed to back scatter by the polarizing and scattering sheet can be avoided to secure visibility, such as a contrast.